How deep do I need to set concrete blocks used as posts @ corners of deck style room addition N.WI.?

Question

I am building a new bed room that is attached to the rear of my home. The 2 outside corners of the deck rest on concrete blocks used as "Posts". With a UN-heated crawl space under the room do I need to worry about frost heaving the concrete blocks? (buried 30" deep. Past clay and back filled with1/2 -3/4" river rock)

Answer 1

Depends on where you live. If you are below or even with Indiana your are probably ok. If you live Michigan,Minnesota,Wisc or in the longitude you may experience freeze heave.

Backfilling up against it as high as you can with good topsoil would help.

Nothing keeps frozen ground from moving blocks,concrete,steel. Expanding frozen soil has pushed concrete slabs sideways 1-2 inches in just one winter. Make sure your roof overhang or guttering does not let water run toward or close to your house.It does not matter in the summer but when cold weather gets close you don't want the ground right around the house all soggy and wet cause when the freeze comes it will expand and heave up/out.

Good Luck

Answer 2

What works for a "deck" will not work for a "house".  You are fishing on thin ice.  I think you should dig 18" diameter holes, make rebar cages 12" in diameter, dig down 3' or perhaps 4' and have the concrete and cages extend up as high as needed to where you will be placing the rim beams on top.  Rebar cages should be 6 pieces of #5 or #6 rebar with 3/8" rebar circles every 9" except at both ends where they should be 2" apart.

Rim Beam: to support the 2x4 walls, 4x12 treated.  Concrete piers should not be more than 12' apart.